Exemplary embodiments of the present invention relate to spark plugs for internal combustion engines, and more particularly to a spark plug configured to be easily indexed and removed from the engine cylinder head.
Spark plugs include a center electrode, an insulator disposed about the center electrode and a metal casing disposed about the insulator. The casing includes a jam nut shell that is hot-pressed to an end portion of a ground shield. The ground shield has a ground strap disposed in a spaced relationship with the center electrode for defining a spark gap therebetween.
The spark plug is indexed by marking the location of the spark gap on a portion of the plug that remains visible when the plug is installed on a cylinder head and then noting the direction in which the mark faces after the plug has been installed. The plug is then removed and re-installed on the cylinder head with additional washers, such that the orientation of the tightened plug is changed for directing the spark gap toward the valves. Such indexing is typically performed individually for each plug, as the orientation of the gap with respect to the threads of the shell can be random.
The spark plug is configured to dispose the ground strap adjacent to a surface of the cylinder head, such that carbon buildup on the ground strap can bind the ground strap to the cylinder head. Accordingly, removal of the spark plug can cause the ground strap to become detached from the ground shield and remain within the cylinder head.
Accordingly, it is desirable to provide a spark plug that is configured to be easily indexed and removed from a cylinder head.